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Up to 20% of pregnant women smoke and there is indirect evidence that certain tobacco-specific metabolites can cross the placental barrier and are genotoxic to the fetus. The presence of micronuclei results from chromosome damage and reflects the degree of underlying genetic instability. Fetal blood was obtained from the cord blood of 143 newborns (102 from nonsmoking mothers and 41 from mothers smoking >10 cigarettes/d during pregnancy).

The micronucleus assay was performed following the guidelines established by the Human MicroNucleus project with modifications. To test the micronucleus assay, we evaluated the effect of a range of benzopyrene-7,8-diol-9,10-epoxide concentrations (from 3.125 nM to 4 microM) on cord blood from nonsmoking mothers. This validation showed that the number of micronuclei and apoptotic cells increased with benzopyrene-7,8-diol-9,10-epoxide dose (p < 0.0001 and p = 0.001, respectively); the minimal detectable effect was induced by 12.5 nM benzopyrene-7,8-diol-9,10-epoxide. In our sample, the number of MN was significantly higher in the 41 cord blood samples from mothers who smoked during pregnancy [smokers: 4 (1; 10.5); nonsmokers: 3 (0; 8); p = 0.016].

Therefore, the data reported herein support the hypothesis that tobacco compounds are able to induce chromosomal losses and breaks that are detectable as an increased number of micronuclei.